Electrode plate, electrochemical apparatus, battery module, battery pack, and device

ABSTRACT

This application relates to an electrode plate that includes a current collector and an electrode active material layer disposed on at least one surface of the current collector. The current collector includes a support layer and a conductive layer disposed on at least one surface of the support layer. A single-side thickness D2 of the conductive layer satisfies 30 nm≤D2≤3 μm. The electrode active material layer includes an electrode active material, a binder, and a conductive agent unevenly distributed in a thickness direction of the electrode active material layer. A weight percentage of the conductive agent in an interior area of the electrode active material layer is higher than that in an exterior area of the electrode active material layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of PCT Patent ApplicationNo. PCT/CN2019/117142, entitled “ELECTRODE PLATE, ELECTROCHEMICALDEVICE, BATTERY MODULE, BATTERY PACK, AND EQUIPMENT” filed on Nov. 11,2019, which claims priority to Chinese Patent Application No.201811644245.2, filed with the State Intellectual Property Office of thePeople's Republic of China on Dec. 29, 2018, and entitled “ELECTRODEPLATE, ELECTROCHEMICAL APPARATUS, BATTERY MODULE, BATTERY PACK, ANDDEVICE”, all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

This application relates to the battery field, and specifically, to anelectrode plate, an electrochemical apparatus, a battery module, abattery pack, and a device.

BACKGROUND

Lithium-ion batteries have advantages such as high energy density, highoutput power, long cycle life, and low environmental pollution, andtherefore are extensively applied in electric vehicles and consumerelectronic products. As the application scope of the lithium-ionbatteries is continuously expanded, people have higher requirements onweight energy density and volume energy density of the lithium-ionbatteries.

To obtain a lithium-ion battery with high weight energy density andvolume energy density, the following improvements are generally made tothe lithium-ion battery: (1) choosing a positive electrode material or anegative electrode material with a high specific discharge capacity; (2)optimizing a mechanical design of the lithium-ion battery to minimize avolume of the lithium-ion battery; (3) selecting a positive electrodeplate or a negative electrode plate with high compacted density; and (4)reducing weights of components of the lithium-ion battery.

Improvements to a current collector generally include selecting acurrent collector with a light weight or small thickness. For example, acurrent collector with punched holes or a plastic current collectorcoated with a metal layer may be used.

For an electrode plate and a battery that use a plastic currentcollector coated with a metal layer, although energy density isincreased, some performance degradations may be caused in terms ofmachinability, safety performance, electrical performance, and the like.To obtain an electrode plate and a current collector with goodelectrochemical performance, a plurality of improvements are stillneeded.

SUMMARY

In view of this, this application provides an electrode plate, anelectrochemical apparatus, a battery module, a battery pack, and adevice

According to a first aspect, this application provides an electrodeplate that has a current collector and an electrode active materiallayer disposed on at least one surface of the current collector. Thecurrent collector includes a support layer and a conductive layerdisposed on at least one surface of the support layer, and a single-sidethickness D2 of the conductive layer satisfies 30 nm≤D2≤3 μm. Theelectrode active material layer includes an electrode active material, abinder, and a conductive agent. The conductive agent is unevenlydistributed in a thickness direction of the electrode active materiallayer, and a weight percentage of the conductive agent in an interiorarea of the electrode active material layer is higher than a weightpercentage of the conductive agent in an exterior area of the electrodeactive material layer.

According to a second aspect, this application relates to anelectrochemical apparatus, including a positive electrode plate, anegative electrode plate, a separator, and an electrolyte, where thepositive electrode plate and/or the negative electrode plate are/or theelectrode plate in the first aspect of this application.

According to a third aspect, this application relates to a batterymodule, including the electrochemical apparatus in the second aspect ofthis application.

According to a fourth aspect, this application relates to a batterypack, including the battery module in the third aspect of thisapplication.

According to a fifth aspect, this application relates to a device,including the electrochemical apparatus in the second aspect of thisapplication, where the electrochemical apparatus is used as a powersupply for the device; and preferably, the device includes a mobiledevice, an electric vehicle, an electric train, a satellite, a ship, andan energy storage system.

The technical solutions of this application have at least the followingbeneficial effects:

The electrode active material layer is divided into two areas in thethickness direction: the interior area and the exterior area.Conductivity of the interior area is higher than that of the exteriorarea. An electrochemical capacity of the exterior area is higher thanthat of the interior area. The interior area of the electrode activematerial layer can improve a composite current collector interface,increase a bonding force between the current collector and the electrodeactive material layer, and ensure that the electrode active materiallayer is more firmly disposed on the surface of the composite currentcollector. In addition, this can properly overcome disadvantages such aspoor conductivity of the composite current collector and vulnerabilityto damage of the conductive layer of the composite current collector.Because a conductive network between the current collector and an activesubstance in the electrode active material layer is effectively repairedand established, electronic transmission efficiency is improved, andresistance between the current collector and the electrode activematerial layer is reduced. Therefore, direct current resistance in acell can be effectively reduced, power performance of the cell isimproved, and it is ensured that phenomena such as great polarizationand lithium precipitation do not easily occur in a long cycling processof the cell, that is, long-term reliability of the cell is effectivelyimproved. Therefore, the electrode plate and electrochemical apparatusin this application have good balanced electrical performance, safetyperformance, and machinability.

Because the electrochemical apparatus is included, the battery module,battery pack, and device in this application have at least the sameadvantages as the electrochemical apparatus.

BRIEF DESCRIPTION OF DRAWINGS

The following describes a positive electrode plate, an electrochemicalapparatus, and beneficial effects thereof in this application in detailwith reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic structural diagram of a positive electrode currentcollector according to a specific embodiment of this application;

FIG. 2 is a schematic structural diagram of a positive electrode currentcollector according to another specific embodiment of this application;

FIG. 3 is a schematic structural diagram of a positive electrode currentcollector according to another specific embodiment of this application;

FIG. 4 is a schematic structural diagram of a positive electrode currentcollector according to another specific embodiment of this application;

FIG. 5 is a schematic structural diagram of a negative electrode currentcollector according to a specific embodiment of this application;

FIG. 6 is a schematic structural diagram of a negative electrode currentcollector according to another specific embodiment of this application;

FIG. 7 is a schematic structural diagram of a negative electrode currentcollector according to another specific embodiment of this application;

FIG. 8 is a schematic structural diagram of a negative electrode currentcollector according to another specific embodiment of this application;

FIG. 9 is a schematic structural diagram of a positive electrode plateaccording to a specific embodiment of this application;

FIG. 10 is a schematic structural diagram of a positive electrode plateaccording to another specific embodiment of this application;

FIG. 11 is a schematic structural diagram of a negative electrode plateaccording to a specific embodiment of this application;

FIG. 12 is a schematic structural diagram of a negative electrode plateaccording to another specific embodiment of this application;

FIG. 13 is a microscopic observation diagram of a surface of a positiveelectrode current collector according to a specific embodiment of thisapplication;

FIG. 14 is a schematic structural diagram of an electrochemicalapparatus according to a specific embodiment of this application;

FIG. 15 is a schematic structural diagram of a battery module accordingto a specific embodiment of this application;

FIG. 16 is a schematic structural diagram of a battery pack according toa specific embodiment of this application;

FIG. 17 is an exploded view of FIG. 16 ; and

FIG. 18 is a schematic diagram of an embodiment of a device using anelectrochemical apparatus as a power supply.

In the drawings:

-   -   1. battery pack;    -   2. upper case;    -   3. lower case;    -   4. battery module;    -   5. electrochemical apparatus;    -   10. positive electrode current collector;    -   101. positive electrode support layer;    -   102. positive electrode conductive layer;    -   103. positive electrode protection layer;    -   11. positive electrode active material layer;    -   20. negative electrode current collector;    -   201. negative electrode support layer;    -   202. negative electrode conductive layer;    -   203. negative electrode protection layer; and    -   21. negative electrode active material layer.

DESCRIPTION OF EMBODIMENTS

The following further describes this application with reference tospecific embodiments. It should be understood that these specificembodiments are merely intended to describe this application but not tolimit the scope of this application.

A first aspect of this application relates to an electrode plate,including a current collector and an electrode active material layerdisposed on at least one surface of the current collector, where thecurrent collector includes a support layer and a conductive layerdisposed on at least one surface of the support layer, a single-sidethickness D2 of the conductive layer satisfies 30 nm≤D2≤3 μm, theelectrode active material layer includes an electrode active material, abinder, and a conductive agent, the conductive agent in the electrodeactive material layer is unevenly distributed in a thickness direction,and based on a total weight of the electrode active material layer, aweight percentage of the conductive agent in an interior area of theelectrode active material layer is higher than a weight percentage ofthe conductive agent in an exterior area of the electrode activematerial layer.

Apparently, the electrode plate may be a positive electrode plate or anegative electrode plate. When the electrode plate is a positiveelectrode plate, correspondingly, the current collector and theelectrode active material layer are respectively a positive electrodecurrent collector and a positive electrode active material layer. Whenthe electrode plate is a negative electrode plate, correspondingly, thecurrent collector and the electrode active material layer arerespectively a negative electrode current collector and a negativeelectrode active material layer.

The current collector used for the electrode plate in the first aspectof this application is a composite current collector, and the compositecurrent collector is formed by at least two materials. Structurally, thecurrent collector includes the support layer and the conductive layerdisposed on the at least one surface of the support layer, and thesingle-side thickness D2 of the conductive layer satisfies 30 nm≤D2≤3μm. Therefore, the conductive layer in the current collector has aconductive function. The thickness D2 of the conductive layer is farless than a thickness of a common metal current collector such as an Alfoil or a Cu foil in the prior art (thicknesses of common Al foil and Cufoil metal current collectors are generally 12 μm and 8 μm). Therefore,weight energy density and volume energy density of an electrochemicalapparatus (for example, a lithium battery) using the electrode plate canbe increased. In addition, when the composite current collector is usedas a positive electrode current collector, safety performance of thepositive electrode plate in nail penetration can also be greatlyimproved.

However, because the conductive layer of the composite current collectoris thin, conductivity of the composite current collector is poorer thanconductivity of a conventional metal current collector (Al foil or Cufoil), and the conductive layer may be easily damaged in an electrodeplate machining process, which further affects electrical performance ofthe electrochemical apparatus. In addition, in an electrode platerolling process or the like, the support layer (polymeric material orpolymeric composite material) of the composite current collector hasgreater bounce than a conventional metal current collector. Therefore, abonding force between the support layer and the conductive layer and abonding force between the composite current collector and the electrodeactive material layer both need to be enhanced preferably throughinterface improvement.

In the electrode plate according to this application, the conductiveagent is unevenly distributed in the thickness direction in theelectrode active material layer disposed on the current collector.Specifically, the electrode active material layer is divided into twoareas in the thickness direction: the interior area and the exteriorarea, and content of the conductive agent in the interior area of theelectrode active material layer is higher than content of the conductiveagent in the exterior area of the electrode active material layer. To bespecific, conductivity of one side (interior area) of the electrodeactive material layer in contact with the current collector is higher.This can properly overcome disadvantages such as poor conductivity ofthe composite current collector and vulnerability to damage of theconductive layer of the composite current collector. Thehigher-conductivity interior area of the electrode active material layereffectively repairs and establishes a conductive network between thecurrent collector and an active substance in the electrode activematerial layer to improve electronic transmission efficiency and reduceresistance of the electrode plate including the composite currentcollector. Therefore, direct current resistance (DCR) in a cell can beeffectively reduced, power performance of the cell is improved, and itis ensured that phenomena such as great polarization and lithiumprecipitation do not easily occur in a long cycling process of the cell,that is, long-term reliability of the cell is effectively improved.

The following describes in detail a structure, material, performance,and the like of the electrode plate (and the current collector in theelectrode plate) in an embodiment of this application.

[Conductive Layer of the Current Collector]

In comparison with a conventional metal current collector, in thecurrent collector in an embodiment of this application, the conductivelayer has a conductive function and a current collection function, andis configured to provide electrons for the electrode active materiallayer.

A material of the conductive layer is selected from at least one of ametal conductive material and a carbon-based conductive material.

The metal conductive material is preferably selected from at least oneof aluminum, copper, nickel, titanium, silver, a nickel-copper alloy,and an aluminum-zirconium alloy.

The carbon-based conductive material is preferably selected from atleast one of graphite, acetylene black, graphene, a carbon nano-tube.

The material of the conductive layer is preferably the metal conductivematerial, that is, the conductive layer is preferably a metal conductivelayer. When the current collector is a positive electrode currentcollector, aluminum is generally used as the material of the conductivelayer. When the current collector is a negative electrode currentcollector, copper is generally used as the material of the conductivelayer.

When conductivity of the conductive layer is poor or the thickness ofthe conductive layer is excessively small, great resistance and greatpolarization are caused in the battery. When the thickness of theconductive layer is excessively great, the conductive layer cannotimprove weight energy density and volume energy density of the battery.

The single-side thickness of the conductive layer is D2, and D2preferably satisfies 30 nm≤D2≤3 μm, more specifically, 300 nm≤D2≤2 μm,and most preferably, 500 nm≤D2≤1.5 μm, to better ensure both a lightweight and good conductivity of the current collector.

In an embodiment of this application, an upper limit of the single-sidethickness D2 of the conductive layer may be 3 μm, 2.5 μm, 2 μm, 1.8 μm,1.5 μm, 1.2 μm, 1 μm, or 900 nm; a lower limit of the single-sidethickness D2 of the conductive layer may be 800 nm, 700 nm, 600 nm, 500nm, 450 nm, 400 nm, 350 nm, 300 nm, 100 nm, 50 nm, or 30 nm. A range ofthe single-side thickness D2 of the conductive layer may include anynumeric value of the upper limit or the lower limit. Specifically, 300nm≤D2≤2 μm. More specifically, 500 nm≤D2≤1.5 μm.

Because the thickness of the conductive layer in this application issmall, damage such as a crack may be easily generated in an electrodeplate preparation process or the like. In this case, the electrodeactive material layer introduced in the electrode plate and having theconductive agent unevenly distributed in the thickness directionaccording to this application may buffer and protect the conductivelayer, and may form “a repair layer” on a surface of the conductivelayer, to improve the bonding force and contact resistance between thecurrent collector and the active material layer.

Generally, a crack exists in the conductive layer of the electrode platein this application. The crack in the conductive layer generally existsin the conductive layer irregularly. It may be a long strip-shapedcrack, or may be a cross-shaped crack, or may be a scattering crack, ormay be a crack that penetrates the entire conductive layer, or may be acrack formed on the surface of the conductive layer. The crack in theconductive layer is generally caused by rolling, an excessively greatamplitude of a tab during welding, an excessively great tension insubstrate rolling-up, or the like in the electrode plate machiningprocess.

The conductive layer may be formed on the support layer by using atleast one of mechanical rolling, bonding, vapor deposition (vapordeposition), and electroless plating (Electroless Plating). The vapordeposition method is preferably a physical vapor deposition (PhysicalVapor Deposition, PVD) method. The vapor deposition method is preferablyat least one of an evaporation method and a sputtering method. Theevaporation method is preferably at least one of a vacuum evaporatingmethod, a thermal evaporation deposition method, and an electron beamevaporation method. The sputtering method is preferably a magnetronsputtering method.

At least one of the vapor deposition method or the electroless platingmethod is preferred, so that bonding between the support layer and theconductive layer is firmer.

[Support Layer of the Current Collector]

In the current collector in an embodiment of this application, thesupport layer has functions of supporting and protecting the conductivelayer. Because the support layer generally uses an organic polymericmaterial, density of the support layer is generally less than density ofthe conductive layer. Therefore, weight energy density of the batterycan be significantly increased in comparison with a conventional metalcurrent collector.

Moreover, a metal layer having a small thickness is used as the metallayer, so that weight energy density of the battery can be furtherincreased. In addition, because the support layer can properly carry andprotect the conductive layer located on the surface of the supportlayer, a common phenomenon of electrode crack for conventional currentcollectors is unlikely to occur.

A material of the support layer is selected from at least one of aninsulating polymeric material, an insulating polymeric compositematerial, a conductive polymeric material, and a conductive polymericcomposite material.

For example, the insulating polymeric material is selected from at leastone of polyamide, polyterephthalate, polyimide, polyethylene,polypropylene, polystyrene, polyvinyl chloride, aramid fiber,polydiformylphenylenediamine, acrylonitrile-butadiene-styrene copolymer,polybutylene terephthalate, poly-p-phenylene terephthamide,polypropylene ethylene), polyoxymethylene, epoxy resin, phenolic resin,polytetrafluoroethylene, p-phenylene sulfide, polyvinylidene fluoride,silicon rubber, polycarbonate, cellulose and a derivative thereof,amylum and a derivative thereof, protein and a derivative thereof,polyvinyl alcohol and a crosslinking agent thereof, and polyethyleneglycol and a crosslinking agent thereof.

For example, the insulating polymeric composite material is selectedfrom a composite material formed by an insulating polymeric material andan inorganic material, where the inorganic material is preferablyselected from at least one of a ceramic material, a glass material, anda ceramic composite material.

For example, the conductive polymeric material is selected from apolymeric polysulfur nitride material, or a doped conjugated polymericmaterial, for example, at least one of polypyrrole, polyacetylene,polyaniline, and polythiophene.

For example, the conductive polymeric composite material is selectedfrom a composite material formed by an insulating polymeric material anda conductive material, where the conductive material is selected from atleast one of a conductive carbon material, a metal material, and acomposite conductive material, the conductive carbon material isselected from at least one of carbon black, a carbon nano-tube,graphite, acetylene black, and graphene, the metal material is selectedfrom at least one of nickel, iron, copper, aluminum, or an alloythereof, and the composite conductive material is selected from at leastone of nickel-coated graphite powder and nickel-coated carbon fiber.

A person skilled in the art may properly select and determine thematerial of the support layer based on factors such as actualrequirements in an application environment and costs. In thisapplication, the material of the support layer is preferably aninsulating polymeric material or an insulating polymeric compositematerial, especially when the current collector is a positive electrodecurrent collector.

When the current collector is a positive electrode current collector, aspecial current collector that is supported by an insulating layer andhas a specific thickness may be used to apparently improve safetyperformance of the battery. Because the insulating layer isnon-conductive, its resistance is great. Therefore, when a short circuitoccurs in the battery in an abnormal case, short circuit resistance canbe increased, and a short circuit current can be greatly reduced.Therefore, heat generated in the short circuit can be greatly reduced,and safety performance of the battery can be improved.

In addition, because the conductive layer is thin, the conductivenetwork is locally cut off in an abnormal case such as nail penetration,to avoid a short circuit in a large area of the electrochemicalapparatus or even in the entire electrochemical apparatus. Therefore,damage caused by nail penetration or the like to the electrochemicalapparatus can be limited to a penetration point, and only “a point opencircuit” is formed, without affecting normal working of theelectrochemical apparatus in a period of time.

A thickness of the support layer is D1, and D1 preferably satisfies 1μm≤D1≤30 μm, and more specifically, 1 μm≤D1≤15 μm.

If the support layer is excessively thin, mechanical strength of thesupport layer is insufficient, and the support layer may easily crack inthe electrode plate machining process or the like. If the support layeris excessively thick, volume energy density of the battery using thecurrent collector is reduced.

An upper limit of the thickness D1 of the support layer may be 30 μm, 25μm, 20 μm, 15 μm, 12 μm, 10 μm, or 8 μm. A lower limit of the thicknessD1 may be 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or 7 μm. A rangeof the thickness D1 of the support layer may include any numeric valueof the upper limit or the lower limit. Specifically, 1 μm≤D1≤15 μm; morespecifically, 2 μm≤D1≤10 μm; and most preferably, 3 μm≤D1≤8 μm.

In addition, the specific thickness in this application can furtherensure that the current collector has great resistance, andsignificantly reduce a battery temperature increase when a short circuitoccurs in the battery. When the conductive layer is made of aluminum,this can further significantly reduce or prevent a thermite reaction ofthe positive electrode current collector, and ensure good safetyperformance of the battery.

In addition, when the conductive layer is a metal conductive layer, aroom-temperature Young's modulus of the support layer preferablysatisfies 20 Gpa≥E≥4 Gpa.

In this application, a method for testing the room-temperature Young'smodulus of the support layer is as follows:

taking a support layer sample, and cutting the sample to 15 mm×200 mm;using a ten-thousandth micrometer to measure a thickness h (μm) of thesample; using a drawing machine tensile machine to perform a tensiletest at a room temperature, setting an initial position, and fixing alength of the sample between jigs to 50 mm; performing stretching at aspeed of 50 mm/min, and recording a load L (N) and a device displacementy (mm) when stretching to crack, where stress c=L/(15*h)*1000, andstrain η=y/50*100; and drawing a stress-strain curve, and taking a curvein an initial linear area, where a slope of the curve is a Young'smodulus E.

Metal is more rigid, that is, less deformed in the electrode platemachining process such as rolling, than a polymeric material orpolymeric composite material. Therefore, to ensure that a deformationdifference between the support layer and the conductive layer is notexcessively great, which may otherwise cause the conductive layer tocrack, the room-temperature Young's modulus of the support layerpreferably satisfies 20 Gpa≥E≥4 Gpa, so that the support layer can havecertain rigidity and that matching of rigidity between the support layerand the conductive layer can be further improved. In this way, it isensured that the deformation difference between the support layer andthe conductive layer is not excessively great in a machining process ofthe current collector and the electrode plate.

Because the support layer has certain rigidity (20 Gpa≥E≥4 Gpa), thecurrent collector is unlikely to deform or extend excessively in themachining process of the current collector and the electrode plate.Therefore, the conductive layer can be firmly bonded to the supportlayer and is unlikely to fall off, and damage of the conductive layercaused by “passive” extension of the conductive layer can be prevented.In addition, the current collector according to this application hascertain tenacity, so that the current collector and the electrode platehave certain capabilities to withstand deformation and do not easilycrack.

However, the Young's modulus of the support layer cannot be excessivelygreat; otherwise, there is difficulty in rolling up and winding, andmachinability becomes poor. When 20 Gpa≥E, it can be ensured that thesupport layer has certain flexibility, and the electrode plate can alsohave a certain capability to withstand deformation.

In addition, a thermal shrinkage rate of the support layer at 90° C. ispreferably not higher than 1.5%. Therefore, thermal stability of thecurrent collector in the electrode plate machining process can be betterensured.

[Protection Layer of the Current Collector]

In some preferred embodiments of this application, the current collectoris further provided with a protection layer. The protection layer isdisposed on one surface of the conductive layer of the current collectoror disposed on two surfaces of the conductive layer of the currentcollector, that is, a surface of the conductive layer away from thesupport layer and a surface facing the support layer.

The protection layer may be a metal protection layer or a metal oxideprotection layer. The protection layer can prevent the conductive layerof the current collector from being broken by chemical corrosion ormechanical damage. In addition, the protection layer can further enhancemechanical strength of the current collector.

Specifically, protection layers are disposed on the two surfaces of theconductive layer of the current collector. A lower protection layer ofthe conductive layer (that is, a protection layer disposed on thesurface of the conductive layer that faces the support layer) can notonly prevent the conductive layer from being damaged and enhancemechanical strength of the current collector, but also enhance thebonding force between the support layer and the conductive layer andprevent film detachment (that is, the conductive layer is detached fromthe support layer).

A technical effect of an upper protection layer of the conductive layer(that is, a protection layer disposed on the surface of the conductivelayer away from the support layer) is mainly to prevent the conductivelayer from being destructed or corroded or the like in the machiningprocess (for example, the surface of the conductive layer may beaffected by immersion in an electrolyte or rolling). In the electrodeplate in this application, the higher-conductivity interior area of theelectrode active material layer is used to repair a possible crackgenerated in a process of rolling, winding, or the like, enhanceconductivity, and compensate for disadvantages of the composite currentcollector used as a current collector. Therefore, the upper protectionlayer of the conductive layer and the interior area of the electrodeactive material layer can cooperate to further protect the conductivelayer, and jointly improve conducting performance of the compositecurrent collector used as a current collector.

Thanks to good conductivity, the metal protection layer can not onlyfurther improve mechanical strength and corrosion resistance of theconductive layer, but also reduce polarization of the electrode plate.For example, a material of the metal protection layer is selected fromat least one of nickel, chromium, a nickel-based alloy, and acooper-based alloy, and is preferably nickel or a nickel-based alloy.

The nickel-based alloy is an alloy formed by adding one or more otherelements to a pure nickel matrix, and is preferably a nickel-chromiumalloy. The nickel-chromium alloy is an alloy formed by metal nickel andmetal chromium. Optionally, a molar ratio of a nickel element to achromium element is 1:99 to 99:1.

The cooper-based alloy is an alloy formed by adding one or more otherelements to a pure cooper matrix, and is preferably a copper-nickelalloy. Optionally, in the copper-nickel alloy, a molar ratio of a nickelelement to a copper element is 1:99 to 99:1.

When metal oxide is used for the protection layer, because the metaloxide has low ductility, a large specific surface area, and greathardness, the protection layer can also provide effective support andprotection for the conductive layer, and have a good technical effectfor improving the bonding force between the support layer and theconductive layer. For example, a material of the metal oxide protectionlayer is selected from at least one of aluminum oxide, cobalt oxide,chromium oxide, and nickel oxide.

When used as a positive electrode current collector, the compositecurrent collector according to this application preferably uses metaloxide as its protection layer to further improve safety performance ofthe positive electrode plate and battery while achieving a goodtechnical effect of support and protection. When used as a negativeelectrode current collector, the composite current collector accordingto this application preferably uses metal as its protection layer tofurther improve conductivity of the electrode plate and kineticperformance of the battery to further reduce polarization of thebattery, while achieving a good technical effect of support andprotection.

A thickness of the protection layer is D3, and D3 preferably satisfiesD3≤ 1/10 D2, and 1 nm≤D3≤200 nm. If the protection layer is excessivelythin, the conductive layer cannot be protected sufficiently. If theprotection layer is excessively thick, weight energy density and volumeenergy density of the battery may be reduced. Specifically, 5 nm≤D3≤500nm; more specifically, 10 nm≤D3≤200 nm; and most preferably, 10 nm≤D3≤50nm.

Materials of the protection layers located on the two surfaces of theconductive layer may be the same or different, and thicknesses thereofmay be the same or different.

Specifically, a thickness of the lower protection layer is less than athickness of the upper protection layer. This helps improve weightenergy density of the battery.

Further optionally, a proportional relationship between a thickness D3″of the lower protection layer and a thickness D3′ of the upperprotection layer is: ½ D3′≤D3″≤⅘ D3′.

When the current collector is a positive electrode current collector,aluminum is generally used as the material of the conductive layer, anda metal oxide material is preferably used as a material of the lowerprotection layer. In comparison with metal used as the material of thelower protection layer, the metal oxide material has greater resistance.Therefore, this type of lower protection layer can further increaseresistance of the positive electrode current collector to some extent,further increase short circuit resistance when a short circuit occurs inthe battery in an abnormal case, and improve safety performance of thebattery. In addition, because a specific surface area of the metal oxideis larger, a bonding force between the lower protection layer made ofthe metal oxide material and the support layer is enhanced. In addition,because the specific surface area of the metal oxide is larger, thelower protection layer can increase roughness of the surface of thesupport layer, enhance the bonding force between the conductive layerand the support layer, and increase overall strength of the currentcollector.

When the current collector is a negative electrode current collector,cooper is generally used as the material of the conductive layer, and ametal material is preferably used as the material of the protectionlayer. More specifically, on a basis of including at least one metalprotection layer, at least one of the lower protection layer and thelower protection layer further includes a metal oxide protection layer,to improve both conductivity and an interface bonding force of thenegative electrode composite current collector.

[Current Collector]

FIG. 1 to FIG. 8 show schematic structural diagrams of currentcollectors used in electrode plates in some embodiments of thisapplication.

Schematic diagrams of positive electrode current collectors are shown inFIG. 1 to FIG. 4 .

In FIG. 1 , a positive electrode current collector 10 includes apositive electrode current collector support layer 101 and positiveelectrode current collector conductive layers 102 that are disposed ontwo opposite surfaces of the positive electrode current collectorsupport layer 101, and further includes positive electrode currentcollector protection layers 103, that is, lower protection layers,disposed on lower surfaces of the positive electrode current collectorconductive layers 102 (that is, surfaces facing the positive electrodecurrent collector support layer 101).

In FIG. 2 , a positive electrode current collector 10 includes apositive electrode current collector support layer 101 and positiveelectrode current collector conductive layers 102 that are disposed ontwo opposite surfaces of the positive electrode current collectorsupport layer 101, and further includes positive electrode currentcollector protection layers 103, that is, lower protection layers andupper protection layers, disposed on two opposite surfaces of thepositive electrode current collector conductive layers 102.

In FIG. 3 , a positive electrode current collector 10 includes apositive electrode current collector support layer 101 and a positiveelectrode current collector conductive layer 102 disposed on one surfaceof the positive electrode current collector support layer 101, andfurther includes a positive electrode current collector protection layer103, that is, a lower protection layer, disposed on a surface of thepositive electrode current collector conductive layer 102 that faces thepositive electrode current collector support layer 101.

In FIG. 4 , a positive electrode current collector 10 includes apositive electrode current collector support layer 101 and a positiveelectrode current collector conductive layer 102 disposed on one surfaceof the positive electrode current collector support layer 101, andfurther includes positive electrode current collector protection layers103, that is, a lower protection layer and an upper protection layer,disposed on two opposite surfaces of the positive electrode currentcollector conductive layer 102.

Likewise, schematic diagrams of negative electrode current collectorsare shown in FIG. 5 to FIG. 8 .

In FIG. 5 , a negative electrode current collector 20 includes anegative electrode current collector support layer 201 and negativeelectrode current collector conductive layers 202 that are disposed ontwo opposite surfaces of the negative electrode current collectorsupport layer 201, and further includes negative electrode currentcollector protection layers 203, that is, lower protection layers,disposed on surfaces of the negative electrode current collectorconductive layers 202 that face the negative electrode current collectorsupport layer 201.

In FIG. 6 , a negative electrode current collector 20 includes anegative electrode current collector support layer 201 and negativeelectrode current collector conductive layers 202 that are disposed ontwo opposite surfaces of the negative electrode current collectorsupport layer 201, and further includes negative electrode currentcollector protection layers 203, that is, lower protection layers andupper protection layers, disposed on two opposite surfaces of thenegative electrode current collector conductive layers 202.

In FIG. 7 , a negative electrode current collector 20 includes anegative electrode current collector support layer 201 and a negativeelectrode current collector conductive layer 202 disposed on one surfaceof the negative electrode current collector support layer 201, andfurther includes a negative electrode current collector protection layer203, that is, a lower protection layer, disposed on the negativeelectrode current collector conductive layer 202 in face of the negativeelectrode current collector support layer 201.

In FIG. 8 , a negative electrode current collector 20 includes anegative electrode current collector support layer 201 and a negativeelectrode current collector conductive layer 202 disposed on one surfaceof the negative electrode current collector support layer 201, andfurther includes negative electrode current collector protection layers203, that is, a lower protection layer and an upper protection layer,disposed on two opposite surfaces of the negative electrode currentcollector conductive layer 202.

Materials of the protection layers located on the two opposite surfacesof the conductive layer may be the same or different, and thicknessesthereof may be the same or different.

For the current collector used for the electrode plate according to thisapplication, conductive layers may be disposed on two opposite surfacesof the support layer, as shown in FIG. 1 , FIG. 2 , FIG. 5 , and FIG. 6; or a conductive layer may be disposed on only one surface of thesupport layer, as shown in FIG. 3 , FIG. 4 , FIG. 7 , and FIG. 8 .

In addition, although the composite current collector used for theelectrode plate in this application preferably includes the protectionlayer of the current collector as shown in FIG. 1 to FIG. 8 , it shouldbe understood that the protection layer of the current collector is nota necessary structure of the current collector. In some embodiments, theused current collector may not include the protection layer of thecurrent collector.

[Electrode Active Material Layer of the Electrode Plate]

The electrode active material layer used for the electrode plate in thisapplication generally includes an electrode active material, a binder,and a conductive agent. Based on a requirement, the electrode activematerial layer may further include other optional additives orauxiliaries.

For the electrode plate in this application, an average particlediameter D50 of the active material in the electrode active materiallayer is preferably 5 μm to 15 μm. If D50 is excessively small, aftercompaction, a porosity of the electrode plate is small anddisadvantageous for infiltration of an electrolyte, and a large specificsurface area of the electrode plate is likely to produce a plurality ofside reactions with the electrolyte, hence reducing reliability of thecell. If D50 is excessively large, great damage may be easily caused tothe composite current collector in an electrode plate compactionprocess. D50 is a corresponding particle diameter when a cumulativevolume percentage of the active material reaches 50%, that is, a medianparticle diameter in volume distribution. For example, D50 may bemeasured by using a laser diffraction particle diameter distributionmeasuring instrument (for example, Malvern Mastersizer 3000).

For a positive electrode plate, various common electrode activematerials in the art (that is, positive electrode active materials) maybe used. For example, for the lithium battery, a positive electrodeactive material may be selected from lithium cobalt oxide, lithiumnickel oxide, lithium manganese oxide, lithium nickel manganese oxide,lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminumoxide, transition metal phosphate, lithium iron phosphate, and the like.However, this application is not limited to these materials, and mayfurther use other conventional well-known materials that can be used aspositive electrode substances of the lithium-ion battery. One of thesepositive electrode active materials may be used alone, or two or moremay be used in combination. Specifically, the positive electrode activematerial may be selected from one or more of LiCoO2, LiNiO2, LiMnO2,LiMn2O4, LiNi⅓Co⅓Mn⅓O2 (NCM333), LiNi0.5Co0.2Mn0.3O2 (NCM523),LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811),LiNi0.85Co0.15Al0.05O2, LiFePO4, and LiMnPO4.

For a negative electrode plate, various common electrode activematerials in the art (that is, negative electrode active materials) maybe used. For example, for the lithium battery, a negative electrodeactive material may be selected from carbon materials such as graphite(artificial graphite or natural graphite), conductive carbon black, andcarbon fiber, metal or semimetal materials or alloys thereof such as Si,Sn, Ge, Bi, Sn, and In, lithium nitride or lithium oxide, lithium metalor a lithium alloy, and the like.

The conductive agent used in the electrode active material layer ispreferably at least one of a conductive carbon material and a metalmaterial.

For example, the conductive carbon material is selected from at leastone of zero-dimensional conductive carbon (such as acetylene black orconductive carbon black), one-dimensional conductive carbon (such as acarbon nano-tube), two-dimensional conductive carbon (such as conductivegraphite or graphene), and three-dimensional conductive carbon (such asreduced graphene oxide); and the metal material is selected from atleast one of aluminum powder, iron powder, and silver powder.

An important feature of the electrode plate in this application is thatthe conductive agent in the electrode active material layer is unevenlydistributed in the thickness direction, that is, the weight percentageof the conductive agent in the electrode active material layer is unevenand varying. More specifically, based on the total weight of theelectrode active material layer, the weight percentage of the conductiveagent in the interior area of the electrode active material layer (whichmay also be referred to as “a lower-layer electrode active material”) ishigher than the weight percentage of the conductive agent in theexterior area of the electrode active material layer (which may also bereferred to as “an upper-layer electrode active material”).Specifically, a weight percentage of an electrochemical active materialin the interior area is lower than a weight percentage of anelectrochemical active material in the exterior area.

In this application, when mentioned, “interior” of the electrode activematerial refers to one side of the electrode active material layer thatis close to the current collector in the thickness direction; and whenmentioned, “exterior” of the electrode active material refers to oneside of the electrode active material layer that is away from thecurrent collector in the thickness direction.

“The conductive agent is unevenly distributed in the thicknessdirection” and “the weight percentage of the conductive agent in theinterior area of the electrode active material layer is higher than theweight percentage of the conductive agent in the exterior area of theelectrode active material layer” may include a plurality of differentembodiments. For example, the weight percentage of the conductive agentin the electrode active material layer may gradually decrease along thethickness direction from the interior area to the exterior area; or theelectrode active material layer is divided into two or more areas(divided into two layers, three layers, or more layers) in the thicknessdirection, and a weight percentage of the conductive agent in an areaclosest to the current collector is higher than a weight percentage ofthe conductive agent in each area away from the current collector. In aspecific embodiment of this application, the electrode active materiallayer is divided into two areas (that is, divided into two electrodeactive material layers) in the thickness direction, and a weightpercentage of the conductive agent in a lower-layer (interior) electrodeactive material is higher than a weight percentage of the conductiveagent in an upper-layer (exterior) electrode active material.

In a preferred embodiment of this application, the electrode activematerial layer is divided into two areas in the thickness direction,that is, the interior area and the exterior area, and based on a totalweight of the electrode active material layer in the interior area, aweight percentage of the conductive agent in the interior area is 10% to99%, preferably, 20% to 80%, and more specifically, 50% to 80%.

Specifically, the conductive agent in the interior area includes atwo-dimensional conductive carbon material, because after thetwo-dimensional conductive carbon material is added, the two-dimensionalconductive carbon material in the interior area of the electrode activematerial layer may generate “horizontal sliding” in the electrode platecompaction process, thereby implementing a buffer function, reducingdestruction caused by the compaction process to the conductive layer ofthe current collector, and reducing a crack. Specifically, a particlediameter D50 of the two-dimensional conductive carbon material is 0.01μm to 0.1 μm. Specifically, the two-dimensional conductive carbonmaterial in the interior area accounts for 1 wt % to 50 wt % of theconductive agent in the interior area, and the remaining conductiveagent may be another type of conductive agent and is preferably azero-dimensional carbon material. The two-dimensional conductive carbonmaterial and the zero-dimensional carbon material may jointly work tobetter improve conductivity of the entire active material layer, and inparticular, the interior area.

Certainly, to better implement the buffer function, the conductive agentin the exterior area also preferably includes a two-dimensionalconductive carbon material.

Because content of the conductive agent is unevenly distributed, contentof the binder and the active material in the electrode active materialmay also change along the thickness direction.

The binder used in the electrode active material layer is selected fromat least one of styrene butadiene rubber, oil-based polyvinylidenefluoride (PVDF), polyvinylidene fluoride copolymer (for example,PVDF-HFP copolymer or PVDF-TFE copolymer), sodium carboxymethylcelullose, polystyrene, polyacrylic acid, polytetrafluoroethylene,polyacrylonitrile, polyimide, water-based PVDF, polyurethane, polyvinylalcohol, polyacrylate, polyacrylic-acid-polyacrylonitrile copolymer, andpolyacrylate-polyacrylonitrile copolymer.

The binder in the interior area is preferably a water-based binder, forexample, at least one of water-based PVDF, acrylic acid, polyurethane,polyvinyl alcohol, polyacrylate, polyacrylic-acid-polyacrylonitrilecopolymer, and polyacrylate-polyacrylonitrile copolymer. Therefore, DCRof the electrochemical apparatus does not increase significantly. Inthis application, a “water-based” polymeric material means that amolecular chain of a polymer completely extends and dissolves in water;and an “oil-based” polymeric material means that a molecular chain of apolymer completely extends and dissolves in an oil-based solvent. Aperson skilled in the art understands that an appropriate surfactant maybe used to dissolve a same type of polymeric material into water and oilseparately, that is, a same type of polymeric material may be made intoa water-based polymeric material and an oil-based polymeric materialseparately by using an appropriate surfactant. For example, a personskilled in the art may change PVDF into water-based PVDF or oil-basedPVDF based on a requirement.

In addition, for the electrode plate in this application, when contentof the binder in the electrode active material layer is high, there isan appropriate bonding force between the active material layer and thecurrent collector. Therefore, in an abnormal case such as nailpenetration, the active material layer can effectively wrap metal burrsgenerated in the conductive layer, to improve safety performance of thebattery in nail penetration. However, if content of the binder isexcessively high, content of the active material is reduced, and this isdisadvantageous for ensuring a high electrochemical capacity of thebattery. Therefore, to further improve safety of the battery and ensurethe high capacity of the battery, a weight percentage of the binder inthe interior area is preferably higher than a weight percentage of thebinder in the exterior area.

In a preferred embodiment of this application, the electrode activematerial layer is divided into two areas in the thickness direction,that is, the interior area and the exterior area, and based on the totalweight of the electrode active material layer in the interior area, theweight percentage of the binder in the interior area is 1% to 90%,preferably, 20% to 80%, and more specifically, 20% to 50%.

In a preferred embodiment of this application, the electrode activematerial layer is divided into two areas in the thickness direction,that is, the interior area and the exterior area, and based on the totalweight of the electrode active material layer in the interior area, theweight percentage of the conductive agent in the interior area is 10% to99%, preferably, 20% to 80%, and more specifically, 50% to 80%; theweight percentage of the binder in the interior area is 1% to 90%,preferably, 20% to 80%, and more specifically, 20% to 50%; and the restis the electrode active material. However, in this embodiment, contentof the electrode active material in the interior area may be 0%.

In another preferred embodiment of this application, the electrode plateis a positive electrode plate, and based on a total weight of theelectrode (positive electrode) active material layer in the interiorarea, content of the conductive agent is preferably 10 wt % to 98 wt %,content of the binder is preferably 1 wt % to 89 wt %, and content ofthe electrode (positive electrode) active material is preferably 1 wt %to 89 wt %.

To further improve safety of the battery in nail penetration,preferably, content of the binder in the exterior area of the electrodeactive material layer (relative to a total weight of the electrodeactive material layer in the exterior area) is not less than 1 wt %,preferably not less than 1.5 wt %. If certain content of the binder inthe exterior area is maintained, the bonding force between the entireactive material layer (including the interior area and the exteriorarea) and the composite current collector is appropriate. Therefore, inan abnormal case such as nail penetration, the entire active materiallayer can effectively wrap metal burrs generated in the conductivelayer, to improve safety performance of the battery in nail penetration.

In a preferred embodiment of this application, the electrode activematerial layer is divided into two areas in the thickness direction,that is, the interior area and the exterior area, where a thickness H(single-side thickness in a case of two-layer coating) of the interiorarea of the electrode active material layer is preferably 0.1 μm to 5μm; and preferably, H/D2 is 0.5:1 to 5:1. If the ratio of H/D2 isexcessively low, the crack of the conductive layer cannot be effectivelyimproved, and conductivity of the electrode plate cannot be effectivelyimproved. If the ratio is excessively high, not only weight energydensity of the battery is reduced, but also DCR of the battery isincreased, and this is disadvantageous for improving kinetic performanceof the battery.

It should be noted that in the embodiment in which the electrode activematerial layer is divided into two areas in the thickness direction,that is, the interior area and the exterior area, electrode activematerials, conductive agents, and binders used in the interior area andthe exterior area may be the same or different. A conductive agentpreferably including a two-dimensional conductive carbon material inthis application and a water-based binder are preferably used in theinterior area. A same or different conductive agent and binder may beused in the exterior area. For the positive electrode plate, thepositive electrode active material in the interior area may be the sameas or different from the positive electrode active material in theexterior area; and the positive electrode active material in theinterior area is preferably a material with high thermal stability, forexample, at least one of lithium iron phosphate, lithium manganese ironphosphate, lithium manganate, lithium manganese phosphate, NCM333, andNCM523.

The electrode active material layer in which the conductive agent isunevenly distributed in the thickness direction may be prepared by usinga known method in the art, for example, by using a multi-layer coatingmethod, for example, a two-layer coating method or a three-layer coatingmethod. However, this application is not limited thereto.

[Electrode Plate]

FIG. 9 to FIG. 12 show schematic structural diagrams of electrode platesin some embodiments of this application.

Schematic diagrams of positive electrode plates are shown in FIG. 9 andFIG. 10 .

In FIG. 9 , a positive electrode plate includes a positive electrodecurrent collector 10 and positive electrode active material layers 11that are disposed on two opposite surfaces of the positive electrodecurrent collector 10, where the positive electrode current collector 10includes a positive electrode current collector support layer 101,positive electrode current collector conductive layers 102 that aredisposed on two opposite surfaces of the positive electrode currentcollector support layer 101, and a positive electrode protection layer103 (not shown in the figure) that is disposed on one side or two sidesof the positive electrode conductive layer 102.

In FIG. 10 , a positive electrode plate includes a positive electrodecurrent collector 10 and a positive electrode active material layer 11that is disposed on one surface of the positive electrode currentcollector 10, where the positive electrode current collector 10 includesa positive electrode current collector support layer 101, a positiveelectrode current collector conductive layer 102 that is disposed on onesurface of the positive electrode current collector support layer 101,and a positive electrode protection layer 103 (not shown in the figure)that is disposed on one side or two sides of the positive electrodeconductive layer 102.

Schematic diagrams of negative electrode plates are shown in FIG. 11 andFIG. 12 .

In FIG. 11 , a negative electrode plate includes a negative electrodecurrent collector 20 and negative electrode active material layers 21that are disposed on two opposite surfaces of the negative electrodecurrent collector 20, where the negative electrode current collector 20includes a negative electrode current collector support layer 201,negative electrode current collector conductive layers 202 that aredisposed on two opposite surfaces of the negative electrode currentcollector support layer 201, and a negative electrode protection layer203 (not shown in the figure) that is disposed on one side or two sidesof the negative electrode conductive layer 202.

In FIG. 12 , a negative electrode plate includes a negative electrodecurrent collector 20 and a negative electrode active material layer 21that is disposed on one surface of the negative electrode currentcollector 20, where the negative electrode current collector 20 includesa negative electrode current collector support layer 201, a negativeelectrode current collector conductive layer 202 that is disposed on onesurface of the negative electrode current collector support layer 201,and a negative electrode protection layer 203 (not shown in the figure)that is disposed on one side or two sides of the negative electrodeconductive layer 202.

As shown in FIG. 9 to FIG. 12 , an electrode active material layer maybe disposed on one surface of a current collector, or may be disposed ontwo surfaces of a current collector.

A person skilled in the art may understand that when a current collectorprovided with conductive layers on both sides is used, both sides of anelectrode plate may be coated (that is, electrode active material layersare disposed on two surfaces of the current collector), or a single sideof the electrode plate may be coated (that is, an electrode activematerial layer is disposed on only one surface of the currentcollector); when a current collector provided with a conductive layeronly on a single side is used, only a single side of an electrode platecan be coated, and only the side of the current collector on which theconductive layer is disposed can be coated with an electrode activematerial layer.

[Electrochemical Apparatus]

A second aspect of this application relates to an electrochemicalapparatus, including a positive electrode plate, a negative electrodeplate, a separator, and an electrolyte, where the positive electrodeplate and/or the negative electrode plate are/or the electrode plateaccording to the first aspect of this application.

The electrochemical apparatus may be a capacitor, a primary battery, ora secondary battery. For example, the electrochemical apparatus may be alithium-ion capacitor, a lithium-ion primary battery, or a lithium-ionsecondary battery. A method for constructing and preparing theelectrochemical apparatus is well known, except that a positiveelectrode plate and/or a negative electrode plate in this applicationare/is used. Because the electrode plate in this application is used,the electrochemical apparatus has improved safety (for example, safetyin nail penetration) and electrical performance. In addition, becausethe electrode plate in this application can be easily machined,manufacturing costs of the electrochemical apparatus using the electrodeplate in this application can be reduced.

In the electrochemical apparatus in this application, specific types andcomposition of the separator and the electrolyte are not specificallylimited, and may be selected based on an actual requirement.Specifically, the separator may be selected from a polyethylene film, apolypropylene film, a polyvinylidene fluoride film, and a multi-layercomposite film thereof. When the battery is a lithium-ion battery, anon-aqueous electrolyte is generally used as its electrolyte. As anon-aqueous electrolyte, a lithium salt solution dissolved in an organicsolvent is generally used. For example, lithium salt is inorganiclithium salt such as LiC₁O₄, LiPF₆, LiBF₄, LiAsF₆, or LiSbF₆, or organiclithium salt such as LiCF₃SO₃, LiCF₃CO₂, Li₂C₂F₄ (SO₃)₂, LiN (CF₃SO₂)₂,LiC (CF₃SO₂)₃, or LiCnF_(2n+1)SO₃ (n≥2). For example, the organicsolvent used for the non-aqueous electrolyte is cyclic carbonate such asethylene carbonate, propylene carbonate, butylene carbonate, or vinylenecarbonate, or chain carbonate such as dimethyl carbonate, diethylcarbonate, or ethyl methyl carbonate, or chain ester such as methylpropionate, or cyclic ester such as γ-butyrolactone, or chain ether suchas dimethoxyethane, diethyl ether, diethylene glycol dimethyl ether, ortriethylene glycol dimethyl ether, or cyclic ether such astetrahydrofuran or 2-methyltetrahydrofuran, or nitrile such asacetonitrile or propionitrile, or a mixture of these solvents.

[Battery Module]

A third aspect of this application relates to a battery module,including any electrochemical apparatus or several electrochemicalapparatuses in the second aspect of this application.

Further, a quantity of electrochemical apparatuses included in thebattery module may be adjusted based on an application and a capacity ofthe battery module.

In some embodiments, referring to FIG. 14 and FIG. 15 , a plurality ofelectrochemical apparatuses 5 in a battery module 4 are arranged insequence along a length direction of the battery module 4. Certainly, anarrangement may be made in any other manner. Further, the plurality ofelectrochemical apparatuses 5 may be fixed by using fasteners.Optionally, the battery module 4 may further include a housing that hasan accommodating space, and the plurality of electrochemical apparatuses5 are accommodated in the accommodating space.

[Battery Pack]

A fourth aspect of this application relates to a battery pack, includingany battery module or several battery modules in the third aspect ofthis application. To be specific, the battery pack includes anyelectrochemical apparatus or several electrochemical apparatuses in thesecond aspect of this application.

A quantity of battery modules in the battery pack may be adjusted basedon an application and a capacity of the battery pack.

In some embodiments, referring to FIG. 16 and FIG. 17 , a battery pack 1may include a battery box and a plurality of battery modules 4 disposedin the battery box. The battery box includes an upper case 2 and a lowercase 3. The upper case 2 can cover the lower case 3 to form a closedspace for accommodating the battery modules 4. The plurality of batterymodules 4 may be arranged in the battery box in any manner.

[Device]

A fifth aspect of this application relates to a device, including anyelectrochemical apparatus or several electrochemical apparatuses in thesecond aspect of this application. The electrochemical apparatus may beused as a power supply for the device.

Specifically, the device may be, but is not limited to, a mobile device(for example, a mobile phone or a notebook computer), an electricvehicle (for example, a full electric vehicle, a hybrid electricvehicle, a plug-in hybrid electric vehicle, an electric bicycle, anelectric scooter, an electric golf vehicle, or an electric truck), anelectric train, a ship, a satellite, an energy storage system, or thelike.

For example, FIG. 18 shows a device including an electrochemicalapparatus in this application. The device is a full electric vehicle, ahybrid electric vehicle, a plug-in hybrid electric vehicle, or the like,and the electrochemical apparatus in this application supplies power tothe device.

Because the electrochemical apparatus provided in this application isincluded, the battery module, battery pack, and device have at least thesame advantages as the electrochemical apparatus. Details are notdescribed again herein.

A person skilled in the art may understand that the foregoingdefinitions or preferred ranges of component selection, componentcontent, and material physicochemical performance parameters inelectrochemical active materials in different embodiments of thisapplication may be randomly combined, and various embodiments obtainedthrough the combination shall still fall within the scope of thisapplication and shall be considered as a part of content disclosed inthis specification.

Unless otherwise specified, various parameters in this specificationhave general meanings well known in the art, and may be measured byusing a method well known in the art. For example, a test may beperformed according to a method provided in an embodiment of thisapplication. In addition, preferred ranges and options of differentparameters provided in various preferred embodiments may be randomlycombined, and it is considered that various combinations obtainedthereby shall fall within the disclosed scope of this application.

The following further describes beneficial effects of this applicationwith reference to embodiments.

Embodiments

1. Preparing a current collector that does not have a protection layer:

A support layer with a certain thickness is selected, and a conductivelayer with a certain thickness is formed on a surface of the supportlayer by vacuum evaporating, mechanical rolling, or bonding.

(1) A formation condition for vacuum evaporating is as follows: Asupport layer that undergoes surface cleaning processing is placed in avacuum plating chamber; a high-purity metal wire in a metal evaporatingchamber is melted and evaporated at a high temperature of 1600° C. to2000° C.; and the evaporated metal passes through a cooling system inthe vacuum plating chamber and is finally deposited on a surface of thesupport layer to form a conductive layer.

(2) A formation condition for mechanical rolling is as follows: A foilof a conductive layer material is placed in a mechanical roller; apressure of 20 t to 40 t is applied to the foil to roll the foil to apredetermined thickness; then the foil is placed on a surface of asupport layer that undergoes surface cleaning processing; and finally,the two are placed in the mechanical roller, and a pressure of 30 t to50 t is applied, so that the two are tightly bonded.

(3) A formation condition for bonding: A foil of a conductive layermaterial is placed in a mechanical roller; a pressure of 20 t to 40 t isapplied to the foil to roll the foil to a predetermined thickness; thena surface of a support layer that undergoes surface cleaning processingis coated with a mixed solution of PVDF and NMP; and finally, aconductive layer with the predetermined thickness is bonded to thesurface of the support layer and dried at 100° C.

2. Preparing a current collector that has a protection layer:

A current collector that has a protection layer is prepared in thefollowing manners:

(1) First, a protection layer is disposed on a surface of a supportlayer by using a vapor deposition method or a coating method; then aconductive layer with a certain thickness is formed by vacuumevaporating, mechanical rolling, or bonding, on the surface of thesupport layer having the protection layer, to prepare a currentcollector that has a protection layer (the protection layer is locatedbetween the support layer and the conductive layer); in addition, on theforegoing basis, another protection layer may be formed on a surface ofthe conductive layer in a direction away from the support layer by usingthe vapor deposition method, an in-situ formation method, or the coatingmethod, to prepare the current collector with protection layers (theprotection layers are located on two opposite surfaces of the conductivelayer).

(2) First, a protection layer is formed on a surface of a conductivelayer by using a vapor deposition method, an in-situ formation method,or a coating method; then the conductive layer having the protectionlayer is disposed on a surface of a support layer by mechanical rollingor bonding, and the protection layer is disposed between the supportlayer and the conductive layer, to prepare a current collector having aprotection layer (the protection layer is located between the supportlayer and the conductive layer); in addition, on the foregoing basis,another protection layer may be formed on a surface of the conductivelayer in a direction away from the support layer by using the vapordeposition method, the in-situ formation method, or the coating method,to prepare the current collector with protection layers (the protectionlayers are located on two opposite surfaces of the conductive layer).

(3) First, a protection layer is formed on a surface of a conductivelayer by using a vapor deposition method, an in-situ formation method,or a coating method; then the conductive layer having the protectionlayer is disposed on a surface of a support layer by mechanical rollingor bonding, and the protection layer is disposed on the surface of theconductive layer away from the support layer, to prepare a currentcollector having a protection layer (the protection layer is located onthe surface of the conductive layer away from the support layer).

(4) First, protection layers are formed on two surfaces of a conductivelayer by using a vapor deposition method, an in-situ formation method,or a coating method; and then the conductive layer having the protectionlayers is disposed on a surface of a support layer by mechanical rollingor bonding, to prepare a current collector having protection layers (theprotection layers are located on two opposite surfaces of the conductivelayer).

(5) On a basis of “preparing a current collector that does not have aprotection layer” above, another protection layer is formed on a surfaceof a conductive layer in a direction away from a support layer by usinga vapor deposition method, an in-situ formation method, or a coatingmethod, to prepare a current collector having a protection layer (theprotection layer is located on the surface of the conductive layer awayfrom the support layer).

In a preparation example, the vapor deposition method uses vacuumevaporating, the in-situ formation method uses in-situ passivating, andthe coating method uses blade coating.

A formation condition for vacuum evaporating is as follows: A samplethat undergoes surface cleaning processing is placed in a vacuum platingchamber; a protection layer material in an evaporating chamber is meltedand evaporated at a high temperature of 1600° C. to 2000° C.; and theevaporated protection layer material passes through a cooling system inthe vacuum plating chamber and is finally deposited on a surface of thesample to form a protection layer.

A formation condition for in-situ passivating is as follows: Aconductive layer is placed in a high-temperature oxidizing environment,where a temperature is controlled to be 160° C. to 250° C., oxygensupplying in the high-temperature environment is maintained, andprocessing time is 30 min, so that a metal oxide protection layer isformed.

A formation condition for gravure coating is as follows: A protectionlayer material and NMP are stirred and mixed; then a sample surface iscoated with a slurry of the protection layer material (solid content is20% to 75%); then a thickness of the coating is controlled by using agravure roller; and finally, the coating is dried at a temperature of100° C. to 130° C.

3. Preparing an Electrode Plate:

(1) Positive Electrode Plate in an Embodiment:

A positive electrode plate that has a lower positive electrode activematerial layer (interior area) and an upper positive electrode activematerial layer (exterior area) is coated by using a two-layer coatingmethod.

A conductive agent (such as conductive carbon black), a binder (such asPVDF or polyacrylic acid), and an optional positive electrode activematerial that are proportioned are dissolved in an appropriate solvent(for example, NMP or water), and stirred evenly to prepare a primerslurry.

Two surfaces of a composite current collector prepared according to theforegoing method are evenly coated with the primer slurry at a coatingspeed of 20 m/min, and a primer layer is dried, where an oventemperature is 70° C. to 100° C., and drying time is 5 min.

After the primer layer is completely dried, 92 wt % positive electrodeactive material, 5 wt % conductive agent Super-P (“SP” for short), and 3wt % PVDF are dissolved in an NMP solvent, and evenly stirred to preparean upper layer slurry; a dry surface of the primer layer is coated withthe upper layer slurry by extrusion coating; and after the coating isdried at 85° C., a positive electrode active material layer is obtained.

Then the current collector having various coating layers is cold-pressedand cut, and dried for four hours under an 85° C. vacuum condition, anda tab is welded, so that a positive electrode plate is obtained.

(2) Comparative Positive Electrode Plate:

It is prepared by using a method similar to the method for preparing apositive electrode plate in the foregoing embodiment. However, an upperlayer slurry is directly applied to a surface of a composite currentcollector, and no lower positive electrode active material layer (primerlayer) is disposed.

(3) Conventional Positive Electrode Plate:

A current collector is an Al foil with a thickness of 12 μm. By using amethod similar to the foregoing method for preparing a comparativepositive electrode plate, an upper layer slurry is directly applied to asurface of the Al foil current collector, and after processing, aconventional positive electrode plate is obtained.

(4) Negative Electrode Plate in an Embodiment:

A negative electrode plate that has a lower negative electrode activematerial layer (interior area) and an upper negative electrode activematerial layer (exterior area) is coated by using a two-layer coatingmethod.

A conductive agent (such as conductive carbon black), a binder (such asPVDF or polyacrylic acid), and an optional negative electrode activematerial that are proportioned are dissolved in an appropriate solvent(for example, NMP or water), and stirred evenly to prepare a primerslurry.

Two surfaces of a composite current collector prepared according to theforegoing method are evenly coated with the primer slurry at a coatingspeed of 20 m/min, and a primer layer is dried, where an oventemperature is 70° C. to 100° C., and drying time is 5 min.

After the primer layer is completely dried, a negative electrode activesubstance artificial graphite, a conductive agent Super-P, a thickeningagent CMC, and a binder SBR are added based on a mass ratio of96.5:1.0:1.0:1.5 to a deionized water solvent, and mixed evenly toprepare an upper layer slurry; a surface of the primer layer is coatedwith the upper layer slurry by extrusion coating; and after the coatingis dried at 85° C., a negative electrode active material layer isobtained.

Then the current collector having various coating layers is cold-pressedand cut, and dried for four hours under a 110° C. vacuum condition, anda tab is welded, so that a negative electrode plate is obtained.

(5) Comparative Negative Electrode Plate:

It is prepared by using a method similar to the method for preparing anegative electrode plate in the foregoing embodiment. However, anupper-layer slurry is directly applied to a surface of a compositecurrent collector, and no lower negative electrode active material layer(primer layer) is disposed.

(6) Conventional Negative Electrode Plate:

A current collector is a Cu foil with a thickness of 8 μm. By using amethod similar to the foregoing method for preparing a comparativenegative electrode plate, an upper-layer slurry is directly applied to asurface of the Cu foil current collector, and after processing, aconventional negative electrode plate is obtained.

4. Preparing a Battery:

Through a conventional battery preparation process, a positive electrodeplate (compacted density: 3.4 g/cm³), a PP/PE/PP separator, and anegative electrode plate (compacted density: 1.6 g/cm³) are woundtogether into a bare cell, and then placed in a battery housing; anelectrolyte (EC-EMC volume ratio: 3:7; LiPF₆: 1 mol/L) is injected; thenafter processes such as sealing and formation, a lithium-ion secondarybattery (hereinafter referred to as the battery for short) is finallyobtained.

5. Battery Testing Method:

(1) Method for Testing Cycle Life of a Lithium-Ion Battery:

The lithium-ion battery is charged and discharged at 45° C., that is,first charged to 4.2 V by using a 1 C current, and then discharged to2.8 V by using a 1 C current, and a discharge capacity in a first cycleis recorded; then the battery is charged and discharged for 1000 cyclesby using 1 C/1 C currents, and a discharge capacity in the 1000^(th)cycle is recorded; the discharge capacity in the 1000^(th) cycle isdivided by the discharge capacity in the first cycle, and a capacityretention rate in the 1000^(th) cycle is obtained.

(2) Method for Testing a DCR Growth Rate:

At 25° C., a secondary battery is adjusted to 50% SOC by using a 1 Ccurrent, and a voltage U1 is recorded. Then the battery is dischargedfor 30 s by using a 4 C current, and a voltage U2 is recorded.DCR=(U1−U2)/4 C. Then the battery is charged and discharged for 500cycles by using 1 C/1 C currents, and DCR in the 500^(th) cycle isrecorded. The DCR in the 500^(th) cycle is divided by the DCR in thefirst cycle, then 1 is subtracted, and a DCR growth rate in the 500^(th)cycle is obtained.

(3) Pin Penetration Test:

A secondary battery (10 samples) is fully charged to a charging cut-offvoltage by using a 1 C current, and then constant-voltage charging isperformed until the current is reduced to 0.05 C. Then charging isstopped. The battery is penetrated at a speed of 25 mm/s in a directionvertical to a battery plate by using a φ8 mm heat-resistant steel pin,where a penetration position is preferably close to a geometric centerin a penetrated surface, and the steel pin stays in the battery. Whethera phenomenon of battery burning or explosion occurs is observed.

6. Test Result and Discussion:

6.1. Function of a Composite Current Collector in Improving WeightEnergy Density of a Battery

Specific parameters of current collectors and electrode plates thereofin various embodiments are shown in Table 1 (no protection layer isdisposed in the current collectors in the embodiments that are listed inTable 1). In Table 1, for a positive electrode current collector, aweight percentage of the current collector is the percentage of a weightof the positive electrode current collector in a unit area in a weightof a conventional positive electrode current collector in a unit area;and for a negative electrode current collector, a weight percentage ofthe current collector is the percentage of a weight of the negativeelectrode current collector in a unit area in a weight of a conventionalnegative electrode current collector in a unit area.

TABLE 1 Weight Thickness percentage of the of the Electrode plateCurrent collector Support layer Conductive layer current current No. No.Material D1 Material D2 collector collector Positive Positive electrodePI 6 μm Al 300 nm 6.6 μm 30.0% electrode plate 1 current collector 1Positive Positive electrode PET 4 μm Al 500 nm 5 μm 24.3% electrodeplate 2 current collector 2 Positive Positive electrode PET 2 μm Al 200nm 2.4 μm 11.3% electrode plate 3 current collector 3 ConventionalConventional / / Al / 12 μm  100% positive positive electrode electrodeplate current collector Negative Negative electrode PET 5 μm Cu 500 nm 6μm 21.6% electrode plate 1 current collector 1 Negative Negativeelectrode PI 2 μm Cu 800 nm 3.6 μm 23.8% electrode plate 2 currentcollector 2 Negative Negative electrode PET 8 μm Cu 1 μm 10 μm 39.6%electrode plate 3 current collector 3 Negative Negative electrode PET 6μm Cu 1.5 μm 9 μm 48.5% electrode plate 4 current collector 4 NegativeNegative electrode PET 4 μm Cu 1.2 μm 6.4 μm 37.3% electrode plate 5current collector 5 Negative Negative electrode PET 10 μm Cu 200 nm 10.4μm 23.3% electrode plate 6 current collector 6 Negative Negativeelectrode PI 8 μm Cu 2 μm 12 μm 65.3% electrode plate 7 currentcollector 7 Conventional Conventional / / Cu / 8 μm  100% negativenegative electrode electrode plate current collector

Based on Table 1, it can be known that weights of both a positiveelectrode current collector and a negative electrode current collectorin this application are reduced to different extents in comparison witha conventional current collector, so that weight energy density of abattery can be increased. However, for a current collector, and inparticular, for a negative electrode current collector, when a thicknessof a conductive layer is greater than 1.5 μm, an extent of weightreduction improved is reduced.

6.2. Function of a Protection Layer in Improving ElectrochemicalPerformance of a Composite Current Collector

On a basis of the current collectors in the embodiments that are listedin Table 1, protection layers are further formed, to facilitate researchon functions of the protection layers in improving electrochemicalperformance of composite current collectors. “Positive electrode currentcollector 2-1” in Table 2 represents a current collector whoseprotection layers are formed based on “positive electrode currentcollector 2” in Table 1. Meanings of numbers of other current collectorsare similar to this.

TABLE 2 Current collector Upper protection layer Lower protection layerElectrode plate No. No. Material D3′ Material D3″ Positive electrodePositive electrode Nickel 10 nm Nickel 8 nm plate 2-1 current collector2-1 oxide oxide Positive electrode Positive electrode Nickel 50 nmNickel 30 nm plate 2-2 current collector 2-2 oxide oxide Negativeelectrode Negative electrode / / Nickel 200 nm plate 4-1 currentcollector 4-1 Negative electrode Negative electrode Nickel 5 nm / /plate 4-2 current collector 4-2 Negative electrode Negative electrodeNickel-based 100 nm / / plate 4-3 current collector 4-3 alloy Negativeelectrode Negative electrode Nickel 10 nm Nickel 10 nm plate 4-4 currentcollector 4-4 Negative electrode Negative electrode Nickel 50 nm Nickel50 nm plate 4-5 current collector 4-5 Negative electrode Negativeelectrode Nickel 100 nm Nickel 50 nm plate 4-6 current collector 4-6

Table 3 shows cycle performance data obtained through measurement afterthe electrode plates listed in Table 2 are assembled into batteries.

TABLE 3 Capacity retention rate in a 1000^(th) cycle at Battery No.Electrode plate 45° C. Battery 1 Conventional negative Conventionalpositive 86.5% electrode plate electrode plate Battery 2 Conventionalnegative Positive electrode 80.7% electrode plate plate 2 Battery 3Conventional negative Positive electrode 85.2% electrode plate plate 2-1Battery 4 Conventional negative Positive electrode 85.4% electrode plateplate 2-2 Battery 5 Negative electrode Conventional positive 86.3% plate4 electrode plate Battery 6 Negative electrode Conventional positive87.1% plate 4-1 electrode plate Battery 7 Negative electrodeConventional positive 86.5% plate 4-2 electrode plate Battery 8 Negativeelectrode Conventional positive 86.7% plate 4-3 electrode plate Battery9 Negative electrode Conventional positive 87.6% plate 4-4 electrodeplate Battery 10 Negative electrode Conventional positive 87.8% plate4-5 electrode plate Battery 11 Negative electrode Conventional positive88.0% plate 4-6 electrode plate

As shown in Table 3, in comparison with a battery 1 using a conventionalpositive electrode plate and a conventional negative electrode plate, abattery using a current collector according to an embodiment of thisapplication has good cycle life, and its cycle performance is equivalentto that of a conventional battery. In particular, for a battery made ofa current collector including a protection layer, in comparison with abattery made of a current collector not including a protection layer, acapacity retention rate of the battery may be further increased, whichindicates that reliability of the battery is higher.

6.3. Function of a Primer Layer (Interior Area) in ImprovingElectrochemical Performance of a Battery

In an embodiment, a two-layer coating method is used to form anelectrode active material layer on a current collector to form anelectrode plate. Therefore, the electrode active material layer isdivided into two parts: an interior area (which may be referred to as “alower electrode active material layer) and an exterior area (which maybe referred to as “an upper electrode active material layer”. Becausecontent of a conductive agent in the lower active material layer ishigher than content of a conductive agent in the upper active materiallayer, the lower electrode active material layer may also be referred toas a conductive primer layer (or primer layer for short).

The following uses a positive electrode plate as an example to describefunctions of factors such as the primer layer and composition of theprimer layer in improving electrochemical performance of a battery.Table 4 shows specific composition and related parameters of batteriesand electrode plates and current collectors that are used in thebatteries in various embodiments and comparative examples. Table 5 showsa performance measurement result of each battery.

TABLE 4 Upper active material Current Conductive layer Electrodecollector Support layer layer Primer layer (exterior plate No. No.Material D1 Material D2 (interior area) area) Comparative Positive PET10 μm Al 1 μm / NCM333, positive electrode 9.8 μm D50, electrode currentand 55 μm plate 20 collector active 4 material layer thickness PositivePositive PET 10 μm Al 1 μm 10% conductive Same as electrode electrodecarbon black, 90% above plate 21 current water-based collectorpolyacrylic acid, 4 and 1.5 μm thickness Positive Positive PET 10 μm Al1 μm 20% conductive Same as electrode electrode carbon black, 80% aboveplate 22 current water-based collector polyacrylic acid, 4 and 1.5 μmthickness Positive Positive PET 10 μm Al 1 μm 50% conductive Same aselectrode electrode carbon black, 50% above plate 23 current water-basedcollector PVDF, and 1.5 μm 4 thickness Positive Positive PET 10 μm Al 1μm 65% conductive Same as electrode electrode carbon black, 35% aboveplate 24 current water-based collector PVDF, and 1.5 μm 4 thicknessPositive Positive PET 10 μm Al 1 μm 80% conductive Same as electrodeelectrode carbon black, 20% above plate 25 current water-based collectorPVDF, and 1.5 μm 4 thickness Positive Positive PET 10 μm Al 1 μm 99%conductive Same as electrode electrode carbon black, 1% above plate 26current water-based collector PVDF, and 1.5 μm 4 thickness PositivePositive PET 10 μm Al 1 μm 65% conductive Same as electrode electrodecarbon black, 35% above plate 27 current oil-based PVDF, collector and1.5 μm 4 thickness Positive Positive PET 10 μm Al 1 μm 80% conductiveSame as electrode electrode carbon black, 20% above plate 28 currentoil-based PVDF, collector and 1.5 μm 4 thickness Positive Positive PET10 μm Al 1 μm 32.5% conductive Same as electrode electrode carbon black,above plate 29 current 32.5% flake collector conductive 4 graphite (0.05μm D50), 35% water-based PVDF, and 1.5 μm thickness Positive PositivePET 10 μm Al 1 μm 65% conductive Same as electrode electrode carbonblack, 35% above plate 30 current water-based collector PVDF, and 500 4nm thickness Positive Positive PET 10 μm Al 1 μm 65% conductive Same aselectrode electrode carbon black, 35% above plate 31 current water-basedcollector PVDF, and 2 μm 4 thickness Positive Positive PET 10 μm Al 1 μm65% conductive Same as electrode electrode carbon black, 35% above plate32 current water-based collector PVDF, and 5 μm 4 thickness

TABLE 5 DCR growth Battery No. Electrode plate rate Battery 20Comparative positive Conventional negative  35% electrode plate 20electrode plate Battery 21 Positive electrode Conventional negative30.9% plate 21 electrode plate Battery 22 Positive electrodeConventional negative  29% plate 22 electrode plate Battery 23 Positiveelectrode Conventional negative  20% plate 23 electrode plate Battery 24Positive electrode Conventional negative  15% plate 24 electrode plateBattery 25 Positive electrode Conventional negative 14.5% plate 25electrode plate Battery 26 Positive electrode Conventional negative  14%plate 26 electrode plate Battery 27 Positive electrode Conventionalnegative 18.5% plate 27 electrode plate Battery 28 Positive electrodeConventional negative 18.2% plate 28 electrode plate Battery 29 Positiveelectrode Conventional negative 12.9% plate 29 electrode plate Battery30 Positive electrode Conventional negative 15.5% plate 30 electrodeplate Battery 31 Positive electrode Conventional negative 14.6% plate 31electrode plate Battery 32 Positive electrode Conventional negative14.1% plate 32 electrode plate

The following can be seen from the foregoing test data:

-   -   1. When a composite current collector with a thin conductive        layer (that is, a comparative positive electrode plate 20 not        including a conductive primer layer because the two-layer        coating method is not used for coating), because the composite        current collector has disadvantages, for example, it has poorer        conductivity than a conventional metal current collector and the        conductive layer of the composite current collector may be        easily damaged, there is great DCR in a battery and a cycle        capacity retention rate is low. After a conductive primer layer        is introduced by using the two-layer coating method, the        conductive primer layer effectively repairs and establishes a        conductive network between the current collector, the conductive        primer layer, and an active substance to improve electronic        transmission efficiency and reduce resistance between the        current collector and an electrode active material layer, so        that the DCR can be effectively reduced.    -   2. As content of a conductive agent in the conductive primer        layer is increased (positive electrode plates 21 to 26), the DCR        of the battery can be improved to a greater extent.    -   3. Given same composition, introduction of a water-based binder        can improve the DCR more apparently than an oil-based binder        (positive electrode plate 24 vs. positive electrode plate 27,        and positive electrode plate 25 vs. positive electrode plate        28).    -   4. Because flake graphite may implement a buffer function,        reduce damage to the conductive layer of the current collector        in a compaction process, and reduce a crack by generating        “horizontal sliding”, introduction of the flake graphite can        further reduce the DCR of the battery (positive electrode plate        24 vs. positive electrode plate 29).    -   5. As a thickness of the conductive primer layer is increased        (positive electrode plate 30 to positive electrode plate 32),        the DCR of the battery can also be improved apparently. However,        an excessively great thickness of the conductive primer layer is        disadvantageous for improving energy density of the battery.

6.4. Impact of an Electrode Active Material in a Primer Layer

In the foregoing embodiment, for ease of research, no electrode activematerial is added to the primer layers. The following uses a positiveelectrode plate as an example to test an impact of introduction of apositive electrode active material in a primer layer on performance of abattery. Refer to Table 6 and Table 7 for specific composition ofelectrode plates and composition of batteries.

TABLE 6 Current Conductive Upper active Electrode collector Supportlayer layer Primer layer material layer plate No. No. Material D1Material D2 (interior area) (exterior area) Comparative Positive PET 10μm Al 1 μm / NCM333, 9.8 μm positive electrode D50, and electrodecurrent 55 μm active plate 20 collector material layer 4 thicknessPositive Positive PET 10 μm Al 1 μm 80% conductive Same as aboveelectrode electrode carbon black, plate 37 current 15% water-basedcollector polyacrylic acid, 4 5% NCM333, and 1.5 μm thickness PositivePositive PET 10 μm Al 1 μm 60% conductive Same as above electrodeelectrode carbon black, plate 38 current 20% water-based collectorpolyacrylic acid, 4 20% NCM333, and 1.5 μm thickness Positive PositivePET 10 μm Al 1 μm 30% conductive Same as above electrode electrodecarbon black, plate 39 current 20% water-based collector polyacrylicacid, 4 50% NCM333, and 1.5 μm thickness Positive Positive PET 10 μm Al1 μm 30% conductive Same as above electrode electrode carbon black,plate 40 current 20% water-based collector polyacrylic acid, 4 50% LFP,and 1.5 μm thickness

TABLE 7 DCR growth Battery No. Electrode plate rate Battery 20Comparative positive Conventional negative  35% electrode plate 20electrode plate Battery 37 Positive electrode Conventional negative14.2% plate 37 electrode plate Battery 38 Positive electrodeConventional negative 14.9% plate 38 electrode plate Battery 39 Positiveelectrode Conventional negative 15.8% plate 39 electrode plate Battery40 Positive electrode Conventional negative 16.5% plate 40 electrodeplate

From the foregoing test data, it can be seen that regardless of whethera primer layer includes an electrode active material, introduction ofthe primer layer can effectively repair and establish a conductivenetwork between a current collector, a conductive primer layer, and anactive substance to improve electronic transmission efficiency andreduce resistance between the current collector and an electrode activematerial layer, so that DCR can be effectively reduced.

6.5. Function of Content of a Binder in an Electrode Active MaterialLayer in Improving Electrochemical Performance of a Battery

Because content of a binder in a primer layer in an interior area isgenerally high, there is a strong bonding force between the primer layerand a current collector. However, a bonding force between an upperelectrode active material layer and the primer layer is affected bycontent of a binder in the upper active material layer. The content ofthe binder in the upper active material layer (exterior area) should bepreferably higher than a lower limit value, so that in an abnormal casesuch as nail penetration, the entire electrode active material layer caneffectively wrap metal burrs generated in the conductive layer, toimprove safety performance of the battery in nail penetration.

From a perspective of safety of the battery in nail penetration, thefollowing uses a positive electrode plate as an example to describe afunction of the content of the binder in the upper electrode activematerial layer in improving electrochemical performance of the battery.

Positive electrode plates are prepared according to the method in theforegoing embodiment, but composition of upper-layer slurries isadjusted. In this way, a plurality of positive electrode plates withdifferent content of binders in upper positive electrode active materiallayers are prepared. Refer to the following tables for specificcomposition of electrode plates.

TABLE 8 Current Conductive Upper active Electrode collector Supportlayer layer Primer layer material layer plate No. No. Material D1Material D2 (interior area) (exterior area) Positive Positive PET 10 μmAl 1 μm 65% conductive NCM811, 6.5 μm electrode electrode carbon black,D50, 55 μm active plate 33 current 35% material layer collectorwater-based thickness, and 0.5 4 PVDF, and 1.5 wt % conductive μmthickness agent PVDF content Positive Positive PET 10 μm Al 1 μm 65%conductive NCM811, 6.5 μm electrode electrode carbon black, D50, 55 μmactive plate 34 current 35% material layer collector water-basedthickness, and 1 4 PVDF, and 1.5 wt % conductive μm thickness agent PVDFcontent Positive Positive PET 10 μm Al 1 μm 65% conductive NCM811, 6.5μm electrode electrode carbon black, D50, 55 μm active plate 35 current35% material layer collector water-based thickness, and 2 4 PVDF, and1.5 wt % conductive μm thickness agent PVDF content Positive PositivePET 10 μm Al 1 μm 65% conductive NCM811, 6.5 μm electrode electrodecarbon black, D50, 55 μm active plate 36 current 35% material layercollector water-based thickness, and 3 4 PVDF, and 1.5 wt % conductiveμm thickness agent PVDF content

TABLE 9 Nail penetration Battery No. Electrode plate test result Battery33 Positive electrode Conventional negative 1 passed and plate 33electrode plate 9 failed Battery 34 Positive electrode Conventionalnegative 6 passed and plate 34 electrode plate 4 failed Battery 35Positive electrode Conventional negative All passed plate 35 electrodeplate Battery 36 Positive electrode Conventional negative All passedplate 36 electrode plate

Table 9 shows nail penetration test results when the foregoing differentpositive electrode plates are assembled into batteries. The resultsindicate that when content of a binder in an upper positive electrodeactive material layer is higher, safety performance of a correspondingbattery in nail penetration is higher. Specifically, based on a totalweight of the upper positive electrode active material layer, thecontent of the binder in the upper positive electrode active materiallayer is not less than 1 wt %, and more specifically, not less than 1.5wt %.

6.6. Surface Morphology of a Composite Current Collector

In a process of preparing a positive electrode plate 24, after coldpressing, a small sample is taken, and a surface of the positiveelectrode plate 24 is cleaned by using a piece of dust-free paper dippedin a DMC solvent, so that a surface of a composite current collector canbe exposed. Then a surface morphology is observed by using a CCDmicroscope instrument. Refer to FIG. 13 for an observation diagram ofthe surface morphology. An obvious crack can be seen from FIG. 13 . Thecrack is intrinsic to a surface of a conductive layer of the compositecurrent collector, but such crack cannot be observed on a surface of aconventional metal current collector. When the conductive layer of thecomposite current collector is thin, a crack easily occurs when apressure is applied to the conductive layer in a cold-pressing processduring electrode plate machining. In this case, if there is a conductiveprimer layer (that is, an interior area), a conductive network betweenthe current collector and an active substance may be effectivelyrepaired and established to improve electronic transmission efficiency,and reduce resistance between the current collector and an electrodeactive material layer. Therefore, direct current resistance in a cellcan be effectively reduced, power performance of the cell is improved,and it is ensured that phenomena such as great polarization and lithiumprecipitation do not easily occur in a long cycling process of the cell,that is, long-term reliability of the cell is effectively improved.Specifically, this is reflected as a significant slowdown of DCR growthand an improvement of battery performance. The foregoing observationresult provides a possible theoretical explanation about a functionalmechanism of the conductive primer layer, but it should be understoodthat this application is not limited to this specific theoreticalexplanation.

A person skilled in the art may understand that the foregoing shows anapplication example of an electrode plate only by using a lithiumbattery as an example in this application; however, the electrode platein this application may also be applied to another type of battery orelectrochemical apparatus, and a good technical effect of thisapplication can still be achieved.

According to the disclosure and instruction of this specification, aperson skilled in the art of this application may further makeappropriate changes or modifications to the foregoing embodiments.Therefore, this application is not limited to the foregoing disclosureand the described specific embodiments, and some changes ormodifications to this application shall also fall within the protectionscope of the claims of this application. In addition, although somespecific terms are used in this specification, these terms are used onlyfor ease of description, and do not constitute any limitation on thisapplication.

What is claimed is:
 1. An electrode plate, comprising: a currentcollector, the current collector comprising: a support layer; a lowerprotective layer disposed on the support layer, the lower protectivelayer comprising a metal, a metal oxide, or both; a conductive layerdisposed on the lower protective layer; and an upper protective layerdisposed on the conductive layer, the upper protective layer comprisinga metal, a metal oxide, or both, and an electrode active material layerdisposed on the upper protective layer, wherein a thickness D1 of thesupport layer satisfies 1 μm≤D1≤30 μm, a single-side thickness D2 of theconductive layer satisfies 30 nm≤D2≤2 μm, a thickness D3 of the upperprotection layer satisfies D3≤ 1/10 D2 and 1 nm≤D3≤200 nm, a thicknessD3″ of the lower protection layer is less than D3 of the upperprotection layer and satisfies ½D3≤D3″≤⅘D3, wherein the electrode activematerial layer comprises an electrode active material, a binder, and aconductive agent, the electrode active material layer is further dividedinto an interior area and an exterior area in a thickness direction, theconductive agent in the electrode active material layer is unevenlydistributed in a thickness direction of the electrode active materiallayer, and based on a total weight of the electrode active materiallayer, a weight percentage of the conductive agent in the interior areaof the electrode active material layer is higher than a weightpercentage of the conductive agent in the exterior area of the electrodeactive material layer, the weight percentage of the conductive agent inthe interior area is at least 50%, the weight percentage of the binderin the interior area is 20% to 50%, the weight percentage of theelectrode active material in the interior area is no more than 50%,based on the total weight of the interior area, and wherein a thicknessH of the interior area is 0.1 μm to 5 μm, and a ratio of H to D2 is0.5:1 to 5:1.
 2. The electrode plate according to claim 1, wherein theconductive layer is a metal conductive layer, and a material of themetal conductive layer is selected from at least one of aluminum,copper, nickel, titanium, silver, a nickel-copper alloy, and analuminum-zirconium alloy; a material of the support layer is selectedfrom at least one of an insulating polymeric material, an insulatingpolymeric composite material, a conductive polymeric material, and aconductive polymeric composite material; the insulating polymericmaterial is selected from at least one of polyamide, polyterephthalate,polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride,aramid fiber, polydiformylphenylenediamine,acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate,poly-p-phenylene terephthamide, polypropylene ethylene),polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene,p-phenylene sulfide, polyvinylidene fluoride, silicon rubber,polycarbonate, cellulose and a derivative thereof, amylum and aderivative thereof, protein and a derivative thereof, polyvinyl alcoholand a crosslinking agent thereof, and polyethylene glycol and acrosslinking agent thereof; the insulating polymeric composite materialis selected from a composite material formed by an insulating polymericmaterial and an inorganic material, wherein the inorganic material isselected from at least one of a ceramic material, a glass material, anda ceramic composite material; the conductive polymeric material isselected from a polymeric polysulfur nitride material, or a dopedconjugated polymeric material, for example, at least one of polypyrrole,polyacetylene, polyaniline, and polythiophene; the conductive polymericcomposite material is selected from a composite material formed by aninsulating polymeric material and a conductive material, wherein theconductive material is selected from at least one of a conductive carbonmaterial, a metal material, and a composite conductive material, theconductive carbon material is selected from at least one of carbonblack, a carbon nano-tube, graphite, acetylene black, and graphene, themetal material is selected from at least one of nickel, iron, copper,aluminum, or an alloy thereof, and the composite conductive material isselected from at least one of nickel-coated graphite powder andnickel-coated carbon fiber; and the material of the support layer is aninsulating polymeric material or an insulating polymeric compositematerial.
 3. The electrode plate according to claim 1, wherein aroom-temperature Young's modulus E of the support layer satisfies 20Gpa≥E≥4 Gpa.
 4. The electrode plate according to claim 1, wherein thethickness D1 of the support layer satisfies 1 μm≤D1≤15 μm.
 5. Theelectrode plate according to claim 1, wherein the single-side thicknessD2 of the conductive layer satisfies 300 nm≤D2≤2 μm.
 6. The electrodeplate according to claim 1, wherein the single-side thickness D2 of theconductive layer satisfies 500 nm≤D2≤1.5 μm.
 7. The electrode plateaccording to claim 1, wherein the thickness D3 of the protection layersatisfies, 10 nm≤D3≤50 nm.
 8. The electrode plate according to claim 1,wherein the conductive agent is at least one of a conductive carbonmaterial and a metal material, wherein the conductive carbon material isselected from at least one of zero-dimensional conductive carbon such asacetylene black or conductive carbon black, one-dimensional conductivecarbon such as a carbon nano-tube, two-dimensional conductive carbonsuch as conductive graphite or graphene, and three-dimensionalconductive carbon such as reduced graphene oxide, and the metal materialis selected from at least one of aluminum powder, iron powder, andsilver powder; and the binder is selected from at least one of styrenebutadiene rubber, oil-based polyvinylidene fluoride (PVDF),polyvinylidene fluoride copolymer (for example, PVDF-HFP copolymer orPVDF-TFE copolymer), sodium carboxymethyl celullose, polystyrene,polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide,water-based PVDF, polyurethane, polyvinyl alcohol, polyacrylate,polyacrylic-acid-polyacrylonitrile copolymer, andpolyacrylate-polyacrylonitrile copolymer.
 9. The electrode plateaccording to claim 1, wherein the conductive agent in the interior areacomprises a two-dimensional conductive carbon material.
 10. Theelectrode plate according to claim 9, wherein the two-dimensionalconductive carbon material in the interior area accounts for 1 wt % to50 wt % of the conductive agent in the interior area.
 11. The electrodeplate according to claim 9, wherein a particle diameter D50 of thetwo-dimensional conductive carbon material is 0.01 μm to 0.1 μm.
 12. Theelectrode plate according to claim 9, wherein the binder in the interiorarea comprises a water-based binder, for example, at least one ofwater-based PVDF, polyacrylic acid, polyurethane, polyvinyl alcohol,polyacrylate, polyacrylic-acid-polyacrylonitrile copolymer, andpolyacrylate-polyacrylonitrile copolymer.
 13. The electrode plateaccording to claim 1, wherein an average particle diameter D50 of theelectrode active material is 5 μm to 15 μm.
 14. The electrode plateaccording to claim 1, wherein based on a total weight of the electrodeactive material layer in the exterior area, a weight percentage of thebinder in the exterior area is not less than 1 wt %.
 15. The electrodeplate according to claim 1, wherein the electrode plate is a positiveelectrode plate, and the active electrode material layer comprises atleast one of lithium cobalt oxide, lithium nickel oxide, lithiummanganese oxide, lithium nickel manganese oxide, lithium nickel cobaltmanganese oxide, lithium nickel cobalt aluminum oxide, transition metalphosphate, and lithium iron phosphate.
 16. The electrode plate accordingto claim 1, wherein the electrode plate is a negative electrode plate,and the active electrode material layer comprises at least one ofgraphite, conductive carbon black, carbon fiber, metal, semimetal, andmetal alloy.